This invention relates in general to a process and more specifically, to a process for preparing and imaging with a flexible electrostatographic imaging member.
Flexible electrostatographic belt imaging members are well known in the art. Typical electrostatographic flexible belt imaging members include, for example, photoreceptors for electrophotographic imaging systems and electroreceptors or ionographic imaging members for electrographic imaging systems. These belts are usually formed by cutting a rectangular sheet from a web, overlapping opposite ends, and welding the overlapped ends together to form a welded seam.
Flexible electrophotographic imaging member belts are usually multilayered photoreceptors that comprise a substrate, an electrically conductive layer, an optional hole blocking layer, an adhesive layer, a charge generating layer, a charge transport layer and an anti-curl backing layer. One type of multilayered photoreceptor comprises a layer of finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating organic resin binder. U.S. Pat. No. 4,265,990 discloses a layered photoreceptor having separate charge generating (photogenerating) and charge transport layers. The charge generating layer is capable of photogenerating electron--hole pairs and injecting the photogenerated holes into the charge transport layer.
Although excellent toner images may be obtained with multilayered belt photoreceptors, it has been found that as more advanced, higher speed electrophotographic copiers, duplicators and printers were developed, cracking of the charge transport layer and/or welded seam was encountered during cycling or when less durable materials are used. Since cracks in the photoreceptor surface cause print defects in the final copy, their appearance shortens the belt service life. Moreover, seam cracking creates a deposition site where toner, carrier, paper debris, and dirt accumulate and eventually cause premature cleaning blade failure during photoreceptor belt machine cycling.
There is also a great need for long service life flexible belt photoreceptors in compact imaging machines that employ small diameter support rollers for photoreceptor belt systems operating in a very confined space. Small diameter support rollers are also highly desirable for simple, reliable copy paper stripping systems which utilize the beam strength of the copy paper to automatically remove copy paper sheets from the surface of photoreceptor belts after toner image transfer. Unfortunately, small diameter rollers, e.g. less than about 0.75 inch (19 mm) diameter, raise the threshold of mechanical performance criteria to such a high level that photoreceptor belt charge transport layer and/or seam failure due to induced bending stress can become unacceptable for multilayered belt photoreceptor applications.
The welded seam of a belt is formed by passing an ultrasonic welding horn along an overlapped joint at a photoreceptor sheet. The welding operation forms a seam "splash" adjacent to seam. The splash, consists of a molten mixture of charge transport layer, charge generation layer, adhesive layer, charge blocking layer, and anti-curl backing layer materials at the overlapped joint. One of the exposed edges of the seam splash forms a 90 degree angle junction with the surface of the charge transport layer. Under dynamic fatigue conditions, the junction between the splash edge and the charge transport surface layer provides a focal point for stress concentration and becomes a point of mechanical integrity failure in the belt. Dynamic fatigue at this stress concentration point facilitates tear initiation through the charge transport layer. This tear then propagates through the weak charge generating layer/adhesive layer interfacial link to produce local seam delamination.
Also, in liquid development systems, induced bending stress coupled with contact with liquid developers accelerates cracking of the charge transport layer and/or welded seam. Frequent photoreceptor delamination seriously impacts the versatility of a photoreceptor and reduces its practical value for automatic electrophotographic copiers, duplicators and printers.
Typical photoreceptor designs usually require an anti-curl backing layer, coated to the back side of the supporting substrate opposite the electrically operative layers, to provide the desired photoreceptor flatness. Without an anti-curl backing layer, a flexible photoreceptor sheet about 16 inches (40.64 centimeters) in width by 48 inches (121.9 centimeters) in length will spontaneously curl upwardly into a 11/2 inch (38.1 millimeters) diameter roll. Although the application of the anti-curl backing layer is solely for the mechanical purpose of counteracting the curl and achieving photoreceptor flatness, the photoreceptor device will possess a substantial internal tensile stress in the charge transport layer as a consequence of the presence of the anti-curl backing layer coating. When cycled in an electrophotographic imaging system employing an active steering roll to control belt walking, the internal stress within the charge transport layer is exacerbated by photoreceptor belt shear stress induced by the steering action of the roll. This steering action leads to the development of ripples in the photoreceptor belt. In a cross section taken transversely of the photoreceptor belt; these ripples resemble a sine wave having an average amplitude of about 7 micrometers with a frequency of periodicity of about 6 ripples per inch belt width, and appear to the naked eye as series of fine rings extending around the circumference of a typical belt having a width of about 34 centimeters. The wave like topology of these ripples in the photoreceptor belt prevents uniform contact between a receiving sheet and toner images carried on the surface of the photoreceptor during toner image transfer and also adversely affects the quality of the final print. Ripples have also been observed to significantly reduce the efficiency of the cleaning blade function which in turn is detrimental to the creation of high quality images in the final print.
Anti-curl backing layers are usually employed on flexible photoreceptors to maintain a flat shape to photoreceptor. Photoreceptors with anti-curl backing layers exhibit less resistance to fatigue during cycling over machine belt support rollers. Fatigue leads to cracking of the charge transport layer as well as seam delamination and thereby shortening of the service life of the photoreceptor belt. Moreover, the presence of the anti-curl backing layer at the overlapped joint increases the volume of molten mass ejected during the ultrasonic seam welding process to form a large seam splash.
The application of an anti-curl backing layer coating during photoreceptor manufacturing represents an additional coating operation which increases the costs and complexity of manufacturing and decreases the photoreceptor production throughput. Since application of an anti-curl backing layer involves additional handling of a photoreceptor web, the extra handling increases the likelihood of creating more coating defects as well as introducing other physical and cosmetic defects such as scratches, creases, wrinkles and the like. Therefore, the application of an anti-curl backing layer leads to a substantial reduction in yield.
Although the foregoing was described in terms of an electrophotographic imaging belt, the problems described are equally applicable to electrographic imaging belts.